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IKE keying daemon charon » History » Version 15

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Martin Willi, 05.05.2009 15:11
fixed tables converted from trac


IKEv2 keying daemon charon

The charon keying daemon was built from scratch to implement the IKEv2 protocol for strongSwan.
It has a fully multi-threaded design to meet todays requirements.

Architecture

      +---------------------------------+       +----------------------------+
      |          Credentials            |       |          Backends          |
      +---------------------------------+       +----------------------------+

       +------------+    +-----------+        +------+            +----------+
       |  receiver  |    |           |        |      |  +------+  | CHILD_SA |
       +----+-------+    | Scheduler |        | IKE- |  | IKE- |--+----------+
            |            |           |        | SA   |--| SA   |  | CHILD_SA |
    +-------+--+         +-----------+        |      |  +------+  +----------+
 <->|  socket  |               |              | Man- |
    +-------+--+         +-----------+        | ager |  +------+  +----------+
            |            |           |        |      |  | IKE- |--| CHILD_SA |
       +----+-------+    | Processor |--------|      |--| SA   |  +----------+
       |   sender   |    |           |        |      |  +------+
       +------------+    +-----------+        +------+

      +---------------------------------+       +----------------------------+
      |               Bus               |       |      Kernel Interface      |
      +---------------------------------+       +----------------------------+
             |                    |                           |
      +-------------+     +-------------+                     V
      | File-Logger |     |  Sys-Logger |                  //////
      +-------------+     +-------------+
Processor The threading is realized with the help of a thread pool (called processor), which contains a fixed amount of precreated threads. All threads in the daemon originate from the processor. To delegate work to a thread, jobs are queued to the processor for asynchronous execution.
Scheduler The scheduler is responsible to execute timed events. Jobs may be queued to the scheduler to get executed at a defined time (e.g. rekeying). The scheduler does not execute the jobs itself, it queues them to the processor.
IKE_SA Manager The IKE_SA manager manages all IKE_SAs. It further handles the synchronization: Each IKE_SA must be checked out strictly and checked in again after use. The manager guarantees that only one thread may check out a single IKE_SA. This allows us to write the (complex) IKE_SAs routines non-threadsave.
IKE_SA The IKE_SA contain the state and the logic of each IKE_SA and handle the messages.
CHILD_SA The CHILD_SA contains state about an IPsec security association and manages them. An IKE_SA may have multiple CHILD_SAs. Communication to the kernel takes place here through the kernel interface.
Kernel Interface The kernel interface installs IPsec security associations, policies, routes and virtual addresses. It further provides methods to enumerate interfaces and may notify the daemon about state changes at lower layers.
Bus The bus receives signals from the different threads and relays them to interested listeners. Debugging signals, but also important state changes or error messages are sent over the bus.
Controller The controller provides a simple API for plugins to control the daemon (e.g. initiate IKE_SA, close IKE_SA, ...).
Backends Backends are pluggable modules which provide configuration. They have to implement an API which the daemon core uses to get configuration.
Credentials Provides trustchain verification and credential serving using registered plugins.

Plugins

The daemon loads plugins at startup. These implement the plugin_t interface (source:src/libstrongswan/plugins/plugin.h). Each plugin registers itself at the daemon to hook in functionality.

  +-------------------------------------+
  | charon                  +---+ +-----+------+
  |                         |   | |   stroke   |
  |                         |   | +-----+------+
  | +-------------+         |   | +-----+------+
  | | bus         |  ---->  | p | |    smp     |
  | +-------------+         | l | +-----+------+
  | +-------------+  <----  | u | +-----+------+
  | | controller  |         | g | |    sql     |
  | +-------------+  ---->  | i | +-----+------+
  | +-------------+         | n | +-----+------+
  | | credentials |  <----  |   | |  eap_aka   |
  | +-------------+         | l | +-----+------+
  | +-------------+  ---->  | o | +-----+------+
  | | backends    |         | a | |  eap_sim   |
  | +-------------+  <----  | d | +-----+------+
  | +-------------+         | e | +-----+------+
  | | eap         |  ---->  | r | |  eap_md5   |
  | +-------------+         |   | +-----+------+
  |                         |   | +-----+------+
  |                         |   | |eap_identity|
  |                         +---+ +-----+------+
  +-------------------------------------+

There is a growing list of available plugins (see source:src/charon/plugins):

stroke The stroke plugin loads credentials from /etc/ipsec.d, reads ipsec.secrets and accepts configurations and control commands from ipsec starter.
smp The smp plugin implements the SMP protocol to control and query the daemon using an XML interface.
sql The sql plugin provides credentials and configurations from a relational database, see SQL.
eap_aka Implements the AKA EAP module implemented completely in software.
eap_sim Implements the SIM EAP module using either a triplet file or a third party card reader library.
eap_md5 Implements the MD5 EAP module (CHAP).
eap_gtc Implements a GTC EAP module to use for PAM authentication.
eap_identity EAP helper module to serve an Identity over EAP before doing EAP authentication.
load_tester Run LoadTests against self or a remote host.
medcli Reads mediation/mediated connections for a client from a simple database.
medsrv Reads mediation connections for a mediation server from a simple database.
nm NetworkManager configuration and control interface.
uci OpenWRT UCI configuration backend.
unit_tester Simple unit testing framework for charon and libstrongswan.